1. Field of the Invention
The present invention relates to an absorbent article for use in disposable diapers and sanitary napkins; more specifically, the present invention relates to a highly absorbable absorbent article of a slim type and a method for producing the same.
2. Description of the Prior Art
In disposable diapers and sanitary napkins, an absorbent article is interposed between a back sheet comprising a fluid- impermeable resin sheet and an inner sheet in direct touch with the skin of a wearer. As the absorbent article, generally, use is made of a mixture of ground pulp and a highly absorbable resin (so-called super absorbent polymers; abbreviated as SAP) such as polyacrylic acid, which mixture is interposed between an upper sheet and a lower sheet, both comprising a thin paper. Because SAP are more highly absorbable than pulp, the absorbent article is superior to an absorbent article where only pulp is interposed between the upper sheet and the lower sheet, in terms of fluid absorptivity. Thus, the absorbent article can be made thin. Additionally because SAP swell after fluid absorption and are then solidified in the form of gel, SAP can securely retain absorbed urine and blood of menstruation inside the absorbent article, to thereby prevent the absorbed fluid from leaking from the article. Furthermore, SAP are a powder (granules) in their dry state, while SAP turn into a gel after fluid absorption. Therefore, an absorbent article with SAP interposed between the upper and lower sheets therein is soft, compared with an absorbent article with only pulp interposed between the upper and lower sheets therefore the absorbent article with SAP can readily be deformed along with the body shape of a wearer. Thus, diapers and sanitary napkins using the absorbent article confer good feeling on wearing.
When the amount of SAP to pulp is increased so as to enhance the absorptivity, the SAP powder in its dry state before fluid absorption moves between the upper and lower sheets when the wearer makes a motion. As result, the SAP distribution may be non-uniform in the absorbent article. When a part with less SAP absorb urine or blood of menstruation, accordingly, the overall absorption effect of the absorbent article is reduced. Additionally, SAP modified into a gel after fluid absorption (after absorbing fluid) moves between the upper and lower sheets, so that the SAP eventually may be gathered and turned into a solid mass and the resulting mass may break the upper and lower sheets resulting in a unpleasant feeling to the wearer.
So as to overcome the problems described above, for example, Japanese Patent Publication No.61-30041, Japanese Patent Provisional Publication No.6-254118, Japanese Patent Publication No.7-73591 and Japanese Utility Model Publication No.63-23078 describe an absorbent article wherein a given amount of a highly absorbable substance is placed at intervals on a sheet whereby the highly absorbable substance is uniformly dispersed on the whole surface of the sheet and a cover sheet with recesses and protrusions formed thereon covers and bonded to the sheet.
In such an absorbent article, the highly absorbable substance is dispersed at a given amount and pressed with the cover sheet to retain the given amount of the highly absorbable substance with no movement from the initial positions. Thus, the transfer of the highly absorbable substance in the absorbent article can be prevented. Furthermore, the thickness of the absorbent article can be made constant. Still, the fluid absorption in volume of the whole absorbent article can be elevated.
When covering the sheet placing the highly absorbable substance thereon with a cover sheet, however, the positioning should be done so as to securely place the highly absorbable substance in the recesses of the cover sheet. Thus, the production of such absorbent article is laborious. So as to secure a large space in which the highly absorbable substance swells, it is required that the depth and diameter of the recesses of the cover sheet should be so enlarged that the volume of each of the recesses is larger than the volume of the given amount of the highly absorbable substance. Hence, the dimension of the thickness of the absorbent article is larger, which limits the slimming of the absorbent article. When the volume of each of the recesses in the cover sheet is small so as to make the absorbent article slim, alternatively, the cover sheet suppresses the swelling of the highly absorbent substance on fluid absorption, causing a reduction in the absorptivity.
The present invention can overcome the conventional problems. It is an object of the present invention to provide a highly absorbable absorbent article of a slim type, capable of preventing the transfer of the highly absorbable substance in the absorbent article and preventing the thickening of the absorbent article by making a space for the highly absorbable substance after fluid absorption to sufficiently swell in the sheets; and a method for producing the same.